1. Field of the Invention
The present invention relates to an output apparatus, a transmitter, a receiver which respectively outputs, transmits and receives PN (Pseudorandom Noise) sequences, a communications system, methods for outputting, transmitting and receiving PN sequences, and a data recording medium. More particularly, the present invention relates to an apparatus and method suitable for outputting PN sequences as spreading codes in CDMA (Code Division Multiple Access) for spread spectrum communications which is useful for satellite communications, cable communications, mobile communications such as cellular telephony and PHS (Personal Handy-phone System), and ranging such as GPS (Global Positioning System), and also to a transmitter, a receiver, a communications system, a PN sequence transmitting method, a PN sequence receiving method, and a data recording medium all of which employ the above apparatus and the method.
2. Description of the Related Art
Spread spectrum communication technology such as CDMA technique has employed PN sequences as spreading sequences for secure communications and efficient sharing of limited radio frequency resources.
Conventionally, the maximum length code (M-sequence), Gold code, Kasami code, and the like have been utilized to generate the PN sequences. Those code systems usually calculate the PN sequences by using linear shift register circuits and EXCLUSIVE-OR circuits. However, it is difficult to establish security of communications because the PN sequences based on the above code system are binary sequences which are cracked easily.
The spread spectrum communications requires synchronization between communication terminals. However, this synchronization involves a trade-off. The trade-off is between enhancing the security of communications and the synchronization of the PN sequences at the receivers.
In industry, there has been demands for technique for outputting PN sequences which realize more enhanced security as compared to the conventional PN sequences. Chaos theory, which is one of growth studies, has been focused on as a theory which realize more enhanced secure CDMA communications by generating hard-to-detect PN sequences.
However, chaos based PN sequences require a receiver to search a target sequence in a huge sequence space for code synchronization. Therefore, a simple code synchronization technique has also been demanded.
The present invention has been made in consideration of the above problems. It is accordingly an object of the present invention to provide an output apparatus for outputting PN (Pseudorandom Noise) sequences, a transmitter, a receiver, a communications system, methods for outputting, transmitting and receiving PN sequences, and a data recording medium.
More particularly, it is an object of the present invention to provide an apparatus and method suitable for outputting PN sequences as spreading codes in CDMA for spread spectrum communications, and a transmitter, a receiver, a communications system, a PN sequence transmitting method, a PN sequence receiving method, and a data recording medium all of which employ the above apparatus and the method.
In order to achieve the above objects, the following inventions will be disclosed in accordance with the principles of the present invention.
A Pseudorandom Noise sequence output apparatus according to the present invention may be an output apparatus, for outputting a Pseudorandom Noise sequence having a length N (1xe2x89xa6N) and being generated using a Chebyshev polynomial
T(a, cos xcex8)=cos(axcex8), for an integer a (2xe2x89xa6a),
which comprises an accepting section, a calculation section and an output section.
The accepting section accepts
an S (1xe2x89xa6S) number of initial values each of which is a real number larger than xe2x88x921 and less than 1
X1, X2, . . . , Xs, and
an S number of degrees each of which is an integral number equal to or larger than 2
p1, p2, . . . , ps.
The calculation section calculates a Pseudorandom Noise sequence having a length N
z[l], z[2], . . . , z[N]
using the accepted initial values, the degrees and recurrence formulas
xj[1]=Xj;
xj[m+1]=T(pj, xj[m]); and
z[n]=Πj=1sT(pj, xj[n]).
The output section outputs the calculated Pseudorandom Noise sequence.
The initial values to be received in the PN sequence output apparatus of the present invention may all be rational numbers.
A transmitter of the present invention comprises a signal accepting section, a sequence output section, a spreading section and a transmitting section.
The signal accepting section accepts a transmission signal to be input therein.
The sequence output section controls the Pseudorandom Noise sequence output apparatus to accept predetermined initial values and predetermined degrees and to output a PN sequence.
The spreading section multiplies the accepted transmission signal sequentially by elements of the output Pseudorandom Noise sequence so as to perform direct spectrum-spreading.
The transmitting section transmits the signal which is direct-spectrum spread.
A receiver of the present invention comprises a signal accepting section, a sequence output section and an inverse spreading section.
The signal receiving section receives the signal transmitted by the transmitter.
The sequence output section controls the PN sequence output apparatus to accepts same initial values as initial values accepted by the transmitter and same degrees as degrees accepted by the transmitter and to output a Pseudorandom Noise sequence.
The inverse spectrum spreading section multiplies the received signal sequentially by inverse number of elements of the output Pseudorandom Noise sequence, perform direct inverse-spectrum spreading, and decrypt the transmission signal accepted by the transmitter.
A receiver of the present invention comprises a signal receiving section, a generation section, a sequence output section, a correlation detection section, and an inverse spreading section.
The signal receiving section receives a signal transmitted from the transmitter.
The generation section generates initial values and degrees.
The sequence output section controls the Pseudorandom Noise sequence output apparatus to accepts the generated initial values and degrees and to output a Pseudorandom Noise sequence.
The correlation detection section multiplies the received signal sequentially by elements of the output Pseudorandom Noise sequence so as to perform correlation detection.
The inverse spreading section multiplies the received signal sequentially by inverse numbers of elements of the Pseudorandom Noise sequence which is in synchronization with the signal by the correlation detection, perform direct-inverse spectrum spreading, and decrypt the transmission signal received by the transmitter, when it is determined that the generated initial values and degrees are same as the initial values and degrees of the transmitter based on a result of the correlation detection.
A communications system of the present invention comprises the transmitter and the receiver which receives a signal transmitted by the transmitter.
A method of outputting a Pseudorandom Noise sequence is an output method for outputting a Pseudorandom Noise sequence having a length N (1xe2x89xa6N) and being generated using a Chebyshev polynomial
T(a, cos xcex8)=cos(axcex8), for an integer a (2xe2x89xa6a), and the method comprising an accepting step, a calculation step and an output step.
In the accepting step, accepted may be
an S (1xe2x89xa6S) number of initial values each of which is a real number larger than xe2x88x921 and less than 1
X1, X2, . . . , Xs; and
an S number degrees each of which is an integral number equal to or larger than 2
p1, p2, . . . , ps.
In the calculation step, calculated is a Pseudorandom Noise sequence having a length N
z[1], z[2], . . . , z[N]
using the accepted initial values, the degrees and recurrence formulas
xj[1]=Xj;
xj[m+1]=T(pj, xj[m]);
z[n]=Πj=1sT(pj, xj[n]).
In the output step, the calculated PN sequence is output.
In the method of outputting a PN sequence according to the present invention, the initial values to be accepted may be rational numbers.
A method of transmitting a signal may comprise a signal accepting step, a sequence outputting step, a spreading step and a transmitting step.
In the signal accepting step, a transmission signal is accepted.
In the sequence outputting step, the method of outputting a PN sequence is controlled to include a step of accepting predetermined initial values and predetermined degrees and to output a Pseudorandom Noise sequence.
In the spreading step, the accepted transmission signal is multiplied sequentially by elements of the output Pseudorandom Noise sequence, and direct spectrum-spreading may be performed.
In the transmitting step, the signal which is direct-spectrum spread is transmitted.
A method of receiving a signal may comprise a signal receiving step, a sequence outputting step, and an inverse spreading step.
In the signal receiving step, a signal is received.
In the sequence output process, the method of outputting a Pseudorandom Noise sequence is controlled to include a step of accepting predetermined initial values and predetermined degrees and to output a PN sequence.
In the inverse spreading step, the received signal is multiplied sequentially by inverse numbers of elements of the Pseudorandom Noise sequence, direct-inverse spectrum spreading is performed, and a transmission signal may be decrypted.
A method of receiving a signal comprises a signal receiving step, a generating step, a sequence output step, a correlation detecting step, and an inverse spreading step.
In the signal receiving step, a signal is received.
In the generating step, initial values and degrees are generated.
In the sequence outputting step, the method of outputting a PN sequence is controlled to include a step of accepting the generated initial values and degrees and to output a Pseudorandom Noise sequence.
In the correlation detecting step, the received signal is multiplied sequentially by elements of the output Pseudorandom Noise sequence, and correlation detection is performed.
In the inverse spreading step, the received signal is multiplied sequentially by inverse numbers of elements of the Pseudorandom Noise sequence which is synchronized with the signal, direct-inverse spectrum spreading may be performed, and a transmission signal is decrypted, in a case where the generated initial values and degrees meet a predetermined condition based on the correlation detection.
A program for realizing processes, to be executed by the PN sequence output apparatus, the transmitter, the receiver and the communications system of the present invention, and realizing the method of outputting a PN sequence, the method of transmitting a signal and the method of receiving a signal, may be recorded on a data recording medium, according to the present invention, such as a compact disk, a floppy disk, a hard disk, a magneto-optical disk, a digital video disk, a magnetic tape and a semiconductor memory.
The program recorded on the data recording medium according to the present invention may be executed by: a general-purpose computer including a storage device, a calculation device, an output device and a communications device; a mobile terminal including a cellular phone, a PHS and a game machine; and a data processor including a parallel calculator. In this structure, those processes to be executed by the PN sequence output apparatus, the transmitter, the receiver and the communications system, and the method of outputting a PN sequence, the method of transmitting a signal and the method of receiving a signal can be realized.
The data recording medium storing the program according to the present invention may be distributed or sold as a single product independent from the data processor.
The program stored on the data recording medium may be transferred using a carrier wave, as a computer data signal.